Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 1. Introduction 2 3 rmnet driver is used for supporting the Multiplexing and aggregation 4 Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm 5 Technologies, Inc. modems. 6 7 This driver can be used to register onto any physical network device in 8 IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator. 9 10 Multiplexing allows for creation of logical netdevices (rmnet devices) to 11 handle multiple private data networks (PDN) like a default internet, tethering, 12 multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends 13 packets with MAP headers to rmnet. Based on the multiplexer id, rmnet 14 routes to the appropriate PDN after removing the MAP header. 15 16 Aggregation is required to achieve high data rates. This involves hardware 17 sending aggregated bunch of MAP frames. rmnet driver will de-aggregate 18 these MAP frames and send them to appropriate PDN's. 19 20 2. Packet format 21 22 a. MAP packet (data / control) 23 24 MAP header has the same endianness of the IP packet. 25 26 Packet format - 27 28 Bit 0 1 2-7 8 - 15 16 - 31 29 Function Command / Data Reserved Pad Multiplexer ID Payload length 30 Bit 32 - x 31 Function Raw Bytes 32 33 Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command 34 or data packet. Control packet is used for transport level flow control. Data 35 packets are standard IP packets. 36 37 Reserved bits are usually zeroed out and to be ignored by receiver. 38 39 Padding is number of bytes to be added for 4 byte alignment if required by 40 hardware. 41 42 Multiplexer ID is to indicate the PDN on which data has to be sent. 43 44 Payload length includes the padding length but does not include MAP header 45 length. 46 47 b. MAP packet (command specific) 48 49 Bit 0 1 2-7 8 - 15 16 - 31 50 Function Command Reserved Pad Multiplexer ID Payload length 51 Bit 32 - 39 40 - 45 46 - 47 48 - 63 52 Function Command name Reserved Command Type Reserved 53 Bit 64 - 95 54 Function Transaction ID 55 Bit 96 - 127 56 Function Command data 57 58 Command 1 indicates disabling flow while 2 is enabling flow 59 60 Command types - 61 0 for MAP command request 62 1 is to acknowledge the receipt of a command 63 2 is for unsupported commands 64 3 is for error during processing of commands 65 66 c. Aggregation 67 68 Aggregation is multiple MAP packets (can be data or command) delivered to 69 rmnet in a single linear skb. rmnet will process the individual 70 packets and either ACK the MAP command or deliver the IP packet to the 71 network stack as needed 72 73 MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding.... 74 MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad... 75 76 3. Userspace configuration 77 78 rmnet userspace configuration is done through netlink library librmnetctl 79 and command line utility rmnetcli. Utility is hosted in codeaurora forum git. 80 The driver uses rtnl_link_ops for communication. 81 82 https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl